Convert from zoned format to decimal floating point format

ABSTRACT

Machine instructions, referred to herein as a long Convert from Zoned instruction (CDZT) and extended Convert from Zoned instruction (CXZT), are provided that read EBCDIC or ASCII data from memory, convert it to the appropriate decimal floating point format, and write it to a target floating point register or floating point register pair. Further, machine instructions, referred to herein as a long Convert to Zoned instruction (CZDT) and extended Convert to Zoned instruction (CZXT), are provided that convert a decimal floating point (DFP) operand in a source floating point register or floating point register pair to EBCDIC or ASCII data and store it to a target memory location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/560,158, filed Dec. 4, 2014, entitled “CONVERT FROM ZONED FORMAT TODECIMAL FLOATING POINT FORMAT”, which is a continuation of Ser. No.13/339,791, filed Dec. 29, 2011, entitled “CONVERT FROM ZONED FORMAT TODECIMAL FLOATING POINT FORMAT”, both of which are hereby incorporatedherein by reference in their entirety.

BACKGROUND

An aspect of the present invention relates, in general, to processingwithin a computing environment, and in particular, to converting datafrom one format to another format.

Data may be stored in internal computer storage or external storage in anumber of different formats, including in Extended Binary Coded DecimalInterchange (EBCDIC), American Standard for Information Interchange(ASCII), and decimal floating point, among others.

Different computer architectures support different data formats and maywish to perform operations on a particular format. In such a case, thedata, which is in one format, may need to be converted to the desiredformat.

Further, traditionally, operations used to process numerical decimaldata stored in EBCDIC or ASCII formats in databases operate directly onstorage. These operations, referred to as storage-to-storage decimaloperations, and the performance of these operations are limited by thelatency of the memory interface. Each operation that is dependent on theresults from a prior operation must wait until the results are writtenout to storage before it may begin. As the gap between memory latencyand processor speed continues to increase, the relative performance ofthese operations continues to decrease.

BRIEF SUMMARY

Shortcomings of the prior art are overcome and advantages are providedthrough the provision of a method of executing a machine instruction ina central processing unit. The method includes, for instance, obtaining,by a processor, a machine instruction for execution, the machineinstruction being defined for computer execution according to a computerarchitecture, the machine instruction including: at least one opcodefield to provide an opcode, the opcode identifying a convert from zonedto decimal floating point function; a first register field designating afirst operand location; a second register field and a displacementfield, wherein contents of a second register designated by the secondregister field are combined with contents of the displacement field toform an address of a second operand; and a sign control used to indicatewhether the second operand has a sign field; and executing the machineinstruction, the executing including: converting the second operand in azoned format to a decimal floating point format; and placing a result ofthe converting in the first operand location.

Computer program products and systems relating to one or more aspects ofthe present invention are also described and may be claimed herein.Further, services relating to one or more aspects of the presentinvention are also described and may be claimed herein.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a computing environment to incorporateand use one or more aspects of the present invention;

FIG. 2A depicts another embodiment of a computing environment toincorporate and use one or more aspects of the present invention;

FIG. 2B depicts further details of the memory of FIG. 2A, in accordancewith an aspect of the present invention;

FIG. 3 depicts an overview of the logic to convert from a zoned formatto a decimal floating point format, in accordance with an aspect of thepresent invention;

FIG. 4 depicts one embodiment of a format of a Convert from Zonedinstruction used in accordance with an aspect of the present invention;

FIG. 5 depicts further details of the logic to convert from zoned todecimal floating point, in accordance with an aspect of the presentinvention;

FIG. 6 depicts an overview of the logic to convert to a zoned formatfrom a decimal floating point format, in accordance with an aspect ofthe present invention;

FIG. 7 depicts one embodiment of a Convert to Zoned from decimalfloating point instruction used in accordance with an aspect of thepresent invention;

FIG. 8 depicts further details of the logic to convert to zoned fromdecimal floating point, in accordance with an aspect of the presentinvention;

FIG. 9 depicts one embodiment of a computer program productincorporating one or more aspects of the present invention;

FIG. 10 depicts one embodiment of a host computer system to incorporateand use one or more aspects of the present invention;

FIG. 11 depicts a further example of a computer system to incorporateand use one or more aspects of the present invention;

FIG. 12 depicts another example of a computer system comprising acomputer network to incorporate and use one or more aspects of thepresent invention;

FIG. 13 depicts one embodiment of various elements of a computer systemto incorporate and use one or more aspects of the present invention;

FIG. 14A depicts one embodiment of the execution unit of the computersystem of FIG. 13 to incorporate and use one or more aspects of thepresent invention;

FIG. 14B depicts one embodiment of the branch unit of the computersystem of FIG. 13 to incorporate and use one or more aspects of thepresent invention;

FIG. 14C depicts one embodiment of the load/store unit of the computersystem of FIG. 13 to incorporate and use one or more aspects of thepresent invention; and

FIG. 15 depicts one embodiment of an emulated host computer system toincorporate and use one or more aspects of the present invention.

DETAILED DESCRIPTION

Different computer architectures may support different data formats, andthe data formats supported may change over time. For instance, machinesoffered by International Business Machines Corporation havetraditionally supported EBCDIC and ASCII formats. Later machines begansupporting decimal floating point (DFP) formats and operations for whichthere is an IEEE Standard (IEEE 754-2008). However, to use the DFPoperations, the EBCDIC and ASCII data is to be converted to DFP.

In accordance with an aspect of the present invention, an efficientmechanism to convert between EBCDIC or ASCII and decimal floating pointis provided. In one example, this mechanism performs the conversionwithout the memory overhead of other techniques.

In one aspect of the present invention, machine instructions areprovided that read EBCDIC or ASCII data (which have a zoned format) frommemory, convert it to the appropriate decimal floating point format, andwrite it to a target floating point register or floating point registerpair. These instructions are referred to herein as a long Convert fromZoned instruction (CDZT) and an extended Convert from Zoned instruction(CXZT).

In a further aspect of the present invention, machine instructions areprovided that convert a decimal floating point (DFP) operand in a sourcefloating point register or floating point register pair to EBCDIC orASCII data, and store it to a target memory location. These instructionsare referred to herein as a long Convert to Zoned instruction (CZDT) andan extended Convert to Zoned instruction (CZXT).

One embodiment of a computing environment to incorporate and use one ormore aspects of the present invention is described with reference toFIG. 1. A computing environment 100 includes, for instance, a processor102 (e.g., a central processing unit), a memory 104 (e.g., main memory),and one or more input/output (I/O) devices and/or interfaces 106 coupledto one another via, for example, one or more buses 108 and/or otherconnections.

In one example, processor 102 is a z/Architecture® processor which ispart of a System z® server offered by International Business MachinesCorporation (IBM®), Armonk, N.Y. The System z® server implements thez/Architecture®, offered by International Business Machines Corporation,which specifies the logical structure and functional operation of thecomputer. One embodiment of the z/Architecture® is described in an IBM®publication entitled, “z/Architecture Principles of Operation,” IBM®Publication No. SA22-7832-08, Ninth Edition, August, 2010, which ishereby incorporated herein by reference in its entirety. In one examplethe server executes an operating system, such as z/OS®, also offered byInternational Business Machines Corporation. IBM®, z/Architecture® andz/OS® are registered trademarks of International Business MachinesCorporation, Armonk, N.Y., USA. Other names used herein may beregistered trademarks, trademarks, or product names of InternationalBusiness Machines Corporation or other companies.

Another embodiment of a computing environment to incorporate and use oneor more aspects of the present invention is described with reference toFIG. 2A. In this example, a computing environment 200 includes, forinstance, a native central processing unit 202, a memory 204, and one ormore input/output devices and/or interfaces 206 coupled to one anothervia, for example, one or more buses 208 and/or other connections. Asexamples, computing environment 200 may include a PowerPC® processor, apSeries® server or an xSeries® server offered by International BusinessMachines Corporation, Armonk, N.Y.; an HP Superdome with Intel ItaniumII® processors offered by Hewlett Packard Co., Palo Alto, Calif.; and/orother machines based on architectures offered by IBM®, Hewlett Packard,Intel, Sun Microsystems or others. PowerPC®, pSeries® and xSeries® areregistered trademarks of International Business Machines Corporation,Armonk, N.Y., USA. Intel® and Itanium II® are registered trademarks ofIntel Corporation, Santa Clara, Calif.

Native central processing unit 202 includes one or more native registers210, such as one or more general purpose registers and/or one or morespecial purpose registers used during processing within the environment.These registers include information that represent the state of theenvironment at any particular point in time.

Moreover, native central processing unit 202 executes instructions andcode that are stored in memory 204. In one particular example, thecentral processing unit executes emulator code 212 stored in memory 204.This code enables the processing environment configured in onearchitecture to emulate another architecture. For instance, emulatorcode 212 allows machines based on architectures other than thez/Architecture®, such as PowerPC® processors, pSeries® servers, xSeries®servers, HP Superdome servers or others, to emulate the z/Architecture®and to execute software and instructions developed based on thez/Architecture®.

Further details relating to emulator code 212 are described withreference to FIG. 2B. Guest instructions 250 comprise softwareinstructions (e.g., machine instructions) that were developed to beexecuted in an architecture other than that of native CPU 202. Forexample, guest instructions 250 may have been designed to execute on az/Architecture® processor 102, but instead are being emulated on nativeCPU 202 (which may be, for example, an Intel® Itanium II® processor). Inone example, emulator code 212 includes an instruction fetching unit 252to obtain one or more guest instructions 250 from memory 204, and tooptionally provide local buffering for the instructions obtained. Italso includes an instruction translation routine 254 to determine thetype of guest instruction that has been obtained and to translate theguest instruction into one or more corresponding native instructions256. This translation includes, for instance, identifying the functionto be performed by the guest instruction and choosing the nativeinstruction to perform that function.

Further, emulator 212 includes an emulation control routine 260 to causethe native instructions to be executed. Emulation control routine 260may cause native CPU 202 to execute a routine of native instructionsthat emulate one or more previously obtained guest instructions and, atthe conclusion of such execution, return control to the instructionfetch routine to emulate the obtaining of the next guest instruction ora group of guest instructions. Execution of the native instructions 250may include loading data into a register from memory 204; storing databack to memory from a register; or performing some type of arithmetic orlogic operation, as determined by the translation routine.

Each routine is, for instance, implemented in software, which is storedin memory and executed by the native central processing unit 202. Inother examples, one or more of the routines or operations areimplemented in firmware, hardware, software or some combination thereof.The registers of the emulated processor may be emulated using registers210 of the native CPU or by using locations in memory 204. Inembodiments, the guest instructions 250, native instructions 256 andemulator code 212 may reside in the same memory or may be disbursedamong different memory devices.

As used herein, firmware includes, e.g., the microcode, millicode and/ormacrocode of the processor. It includes, for instance, thehardware-level instructions and/or data structures used inimplementation of higher level machine code. In one embodiment, itincludes, for instance, proprietary code that is typically delivered asmicrocode that includes trusted software or microcode specific to theunderlying hardware and controls operating system access to the systemhardware.

In one example, a guest instruction 250 that is obtained, translated andexecuted is one of the instructions described herein. The instruction,which is a z/Architecture® instruction in this example, is fetched frommemory, translated and represented as a sequence of native instructions256 (e.g., PowerPC®, pSeries®, xSeries®, Intel®, etc.) which areexecuted.

In another embodiment, one or more of the instructions are executed inanother architecture environment, including, for example, anarchitecture as described in the “Intel® 64 and IA-32 ArchitecturesSoftware Developer's Manual Volume 1,” Order No. 253665-022US, November2006; “Intel® 64 and IA-32 Architecture Software Developer's ManualVolume 2A,” Order No. 253666-022US, November 2006; the “Intel® Itanium®Architecture Software Developer's Manual Volume 1,” Doc. No. 245317-005,January 2006; the “Intel® Itanium® Architecture Software Developer'sManual Volume 2,” Doc. No. 245318-005, January 2006; and/or the “Intel®Itanium® Architecture Software Developer's Manual Volume 3,” Doc. No.245319-005, January 2006; each of which is hereby incorporated herein byreference in its entirety.

The processors described herein, as well as others, execute instructionsto perform certain functions, such as, for example, converting betweenEBCDIC or ASCII and decimal floating point formats. In one example, theEBCDIC or ASCII data has a zoned format, and therefore, exampleinstructions include, for instance, convert from zoned to decimalfloating point instructions, as well as convert to zoned from decimalfloating point instructions, as described herein.

Prior to describing the instructions, however, various data formatsreferred to herein are described. For instance, in the zoned format, therightmost four bits of a byte are called the numeric bits (N) andnormally include a code representing a decimal digit. The leftmost fourbits of a byte are called the zone bits (Z), except for the rightmostbyte of a decimal operand, where these bits may be treated either as azone or as a sign (S).

Decimal digits in the zoned format may be part of a larger characterset, which includes also alphabetic and special characters. The zonedformat is, therefore, suitable for input, editing, and output of numericdata in human-readable form. In one embodiment, decimal-arithmeticinstructions do not operate directly on decimal numbers in the zonedformat; such numbers are first converted to, for instance, one of thedecimal floating point formats.

Decimal floating point data may be represented in any of three dataformats: short, long, or extended. The contents of each data formatrepresent encoded information. Special codes are assigned to distinguishfinite numbers from NaNs (Not-a-Number) and infinites.

For finite numbers, a biased exponent is used in the format. For eachformat, a different bias is used for right-units-view (RUV) exponentsfrom that for left-units-view (LUV) exponents. The biased exponents areunsigned numbers. The biased exponent is encoded with the leftmost digit(LMD) of the significand in the combination field. The remaining digitsof the significand are encoded in the encoded trailing-significandfield.

Examples of these data formats are:

When an operand in the DFP short format is loaded into a floating-pointregister, it occupies the left half of the register, and the right halfremains unchanged.

When an operand in the DFP long format is loaded into a floating-pointregister, it occupies the entire register.

An operand in the DFP extended format occupies a floating point registerpair. The leftmost 64 bits occupy the entire lower-numbered register ofthe pair and the rightmost 64 bits occupy the entire higher-numberedregister.

The sign bit is in bit 0 of each format, and is, for instance, zero forplus and one for minus.

For finite numbers, the combination field includes the biased exponentand the leftmost digit of the significand; for NaNs and infinities, thisfield includes codes to identify them.

When bits 1-5 of the format are in the range of 00000-11101, the operandis a finite number. The two leftmost bits of the biased exponent and theleftmost digit of the significand are encoded in bits 1-5 of the format.Bit 6 through the end of the combination field include the rest of thebiased exponent.

When bits 1-5 of the format field are 11110, the operand is an infinity.All bits in the combination field to the right of bit 5 of the formatconstitute the reserved field for infinity. A nonzero value in thereserved field is accepted in a source infinity; the reserved field isset to zero in a resultant infinity.

When bits 1-5 of the format are 11111, the operand is a NaN and bit 6,called the SNaN bit, further distinguishes QNaN from SNaN. If bit 6 iszero, then it is QNaN; otherwise, it is SNaN. All bits in thecombination field to the right of bit 6 of the format constitute thereserved field for NaN. A nonzero value in the reserved field isaccepted in a source NaN; the reserved field is set to zero in aresultant NaN.

The below table summarizes the encoding and layout of the combinationfield. In the table, the biased exponent of a finite number is theconcatenation of two parts: (1) two leftmost bits are derived from bits1-5 of the format, and (2) the remaining bits in the combination field.For example, if the combination field of the DFP short format contains10101010101 binary, it represents a biased exponent of 10010101 binaryand a leftmost significand digit of 5.

Bits Bit Biased 1 2 3 4 5 6 Type Exponent LMD 00000 m Finite Number 00

 RBE 0 00001 m Finite Number 00

 RBE 1 00010 m Finite Number 00

 RBE 2 00011 m Finite Number 00

 RBE 3 00100 m Finite Number 00

 RBE 4 00101 m Finite Number 00

 RBE 5 00110 m Finite Number 00

 RBE 6 00111 m Finite Number 00

 RBE 7 01000 m Finite Number 01

 RBE 0 01001 m Finite Number 01

 RBE 1 01010 m Finite Number 01

 RBE 2 01011 m Finite Number 01

 RBE 3 01100 m Finite Number 01

 RBE 4 01101 m Finite Number 01

 RBE 5 01110 m Finite Number 01

 RBE 6 01111 m Finite Number 01

 RBE 7 10000 m Finite Number 10

 RBE 0 10001 m Finite Number 10

 RBE 1 10010 m Finite Number 10

 RBE 2 10011 m Finite Number 10

 RBE 3 10100 m Finite Number 10

 RBE 4 10101 m Finite Number 10

 RBE 5 10110 m Finite Number 10

 RBE 6 10111 m Finite Number 10

 RBE 7 11000 m Finite Number 00

 RBE 8 11001 m Finite Number 00

 RBE 9 11010 m Finite Number 01

 RBE 8 11011 m Finite Number 01

 RBE 9 11100 m Finite Number 10

 RBE 8 11101 m Finite Number 10

 RBE 9 11110 r Infinity¹ — — 11111 0 QNaN² — — 11111 1 SNaN² — —Explanation: — Not applicable.

 Concatenation. ¹All bits in the combination field to the right of bit 5of the format constitute the reserved field for infinity. ²All bits inthe combination field to the right of bit 6 of the format constitute thereserved field for NaN. LMD Leftmost digit of the significand. m Bit 6is a part of the remaining biased exponent. RBE Remaining Biasedexponent. It includes all bits in the combination field to the right ofbit 5 of the format. r Bit 6 is a reserved bit for infinity.

The encoded trailing significand field includes an encoded decimalnumber, which represents digits in the trailing significand. Thetrailing significand includes all significand digits, except theleftmost digit. For infinities, nonzero trailing-significand digits areaccepted in a source infinity; all trailing-significand digits in aresultant infinity are set to zeros, unless otherwise stated. For NaNs,this field includes diagnostic information called the payload.

The encoded trailing significand field is a multiple of 10-bit blockscalled declets. The number of declets depends on the format. Each decletrepresents three decimal digits in a 10-bit value.

The values of finite numbers in the various formats are shown in thefollowing table:

Value Format Left-Units View Right-Units View Short

 10^(e-95)

 (d₀.d₁d₂. . .d₆)

 10^(e-101)

 (d₀d₁d₂. . .d₆) Long

 10^(e-383)

 (d₀.d₁d₂. . .d₁₅)

 10^(e-398)

 (d₀d₁d₂. . .d₁₅) Extended

 10^(e-6143)

 (d₀.d₁d₂. . .d₃₃)

 10^(e-6176)

 (d₀d₁d₂. . .d₃₃) Explanation: d₀.d₁d₂. . .d_(p-1) Significand inleft-units view. The decimal point is to the immediate right of theleftmost digit and d₁ is a decimal digit, where 0

 i

 (p-1) and p is the format precision. d₀d₁d₂. . . d_(p-1) Significand inright-units view. The decimal point is to the right of the rightmostdigit and d₁ is a decimal digit, where 0

 i

 (p-1) and p is the format precision. e Biased exponent.

The term significand is used to mean, for instance, the following:

-   -   1. For finite numbers, the significand includes all trailing        significand digits padded on the left with the leftmost digit of        significand derived from the combination field.    -   2. For infinities and NaNs, the significand contains all        trailing significand digits padded on the left with a zero        digit.

For a finite number, the DFP significant digits begin with the leftmostnonzero significand digit and end with the rightmost significand digit.

For a finite number, the number of DFP significant digits is thedifference of subtracting the number of leading zeros from the formatprecision. The number of leading zeros is the number of zeros in thesignificand to the left of the leftmost nonzero digit.

In addition to the above, there is a densely packed decimal (DPD)format. Examples of a mapping of a 3-digit decimal number (000-999) to a10-bit value, called a declet is shown in the table below. The DPDentries are shown in hexadecimal. The first two digits of the decimalnumber are shown in the leftmost column and the third digit along thetop row.

0 1 2 3 4 5 6 7 8 9 00_ 000 001 002 003 004 005 006 007 008 009 01_ 010011 012 013 014 015 016 017 018 019 02_ 020 021 022 023 024 025 026 027028 029 03_ 030 031 032 033 034 035 036 037 038 039 04_ 040 041 042 043044 045 046 047 048 049 05_ 050 051 052 053 054 055 056 057 058 059 06_060 061 062 063 064 065 066 067 068 069 07_ 070 071 072 073 074 075 076077 078 079 08_ 00A 00B 02A 02B 04A 04B 06A 06B 04E 04F 09_ 01A 01B 03A03B 05A 05B 07A 07B 05E 05F 10_ 080 081 082 083 084 085 086 087 088 089

90_ 08C 08D 18C 18D 28C 28D 38C 38D 0AE 0AF 91_ 09C 09D 19C 19D 29C 29D39C 39D 0BE 0BF 92_ 0AC 0AD 1AC 1AD 2AC 2AD 3AC 3AD 1AE 1AF 93_ 0BC 0BD1BC 1BD 2BC 2BD 3BC 3BD 1BE 1BF 94_ 0CC 0CD 1CC 1CD 2CD 2CD 3CC 3CD 2AE2AF 95_ 0DC 0DD 1DC 1DD 2DC 2DD 3DC 3DD 2BE 2BF 96_ 0EC 0ED 1EC 1ED 2EC2ED 3EC 3ED 3AE 3AF 97_ 0FC 0FD 1FC 1FD 2FC 2FD 3FC 3FD 3BE 3BF 98_ 08E08F 18E 18F 28E 28F 38E 38F 0EE 0EF 99_ 09E 09F 19E 19F 29E 29F 39E 39F0FE 0FF

Examples of the mapping of the 10-bit declet to a 3-digit decimal numberis shown in the table below. The 10-bit declet value is split into a6-bit index shown in the left column and a 4-bit index shown along thetop row, both represented in hexadecimal.

0 1 2 3 4 5 6 7 8 9 A B C D E F 00_ 000 001 002 003 004 005 006 007 008009 080 081 800 801 880 881 01_ 010 011 012 013 014 015 016 017 018 019090 091 810 811 890 891 02_ 020 021 022 023 024 025 026 027 028 029 082083 820 821 808 809 03_ 030 031 032 033 034 035 036 037 038 039 092 093830 831 818 819 04_ 040 041 042 043 044 045 046 047 048 049 084 085 840841 088 089 05_ 050 051 052 053 054 055 056 057 058 059 094 095 850 851098 099 06_ 060 061 062 063 064 065 066 067 068 069 086 087 860 861 888889 07_ 070 071 072 073 074 075 076 077 078 079 096 097 870 871 898 89908_ 100 101 102 103 104 105 106 107 108 109 180 181 900 901 980 981 09_110 111 112 113 114 115 116 117 118 119 190 191 910 911 990 991 0A_ 120121 122 123 124 125 126 127 128 129 182 183 920 921 908 909

37_ 670 671 672 673 674 675 676 677 678 679 696 697 876 877  898*  899*38_ 700 701 702 703 704 705 706 707 708 709 780 781 906 907 986 987 39_710 711 712 713 714 715 716 717 718 719 790 791 916 917 996 997 3A_ 720721 722 723 724 725 726 727 728 729 782 783 926 927 968 969 3B_ 730 731732 733 734 735 736 737 738 739 792 793 936 937 978 979 3C_ 740 741 742743 744 745 746 747 748 749 784 785 946 947 788 789 3D_ 750 751 752 753754 755 756 757 758 759 794 795 956 957 798 799 3E 760 761 762 763 764765 766 767 768 768 786 787 966 967  988*  989* 3F_ 770 771 772 773 774775 776 777 778 779 796 797 976 977  998*  999* *Result mapped from anoncanonical declet.

In accordance with an aspect of the present invention, instructions areprovided to convert from zoned format to decimal floating point. In oneembodiment, there are two types of convert from zoned to decimalfloating point instructions, including a long Convert from Zonedinstruction (CDZT), and an extended Convert from Zoned instruction(CXZT), each of which is described below. These instructions provide anefficient means for converting data from EBCDIC or ASCII directly inmemory to the decimal floating point formats in a register.

For instance, referring to FIG. 3, in one embodiment, each machineinstruction reads EBCDIC or ASCII data from memory, STEP 300; convertsit to the appropriate decimal floating point format, STEP 302; andwrites it to a target floating point register or floating point registerpair, STEP 304.

The long Convert from Zoned instruction, CDZT, reads the operand datafrom a specified memory location, converts it to a double precision DFPoperand with a zero exponent, and writes it to the specified targetfloating point register. The extended Convert from Zoned instruction,CXZT, reads the operand data from a specified memory location, convertsit to an extended precision DFP operation with a zero exponent, andwrites it to the specified target floating point register pair. Thenumber of bytes in the source memory location is specified in aninstruction and can be from 1 to 16 bytes for CDZT or from 1 to 34 bytesfor CXZT. The digits of the source operand are all checked for validdigit codes. A sign field in the instruction indicates that the signnibble of the source operand is to be processed. If the sign field isset, the sign is checked for a valid sign code. Assuming it is valid,the sign of the DFP result is set to the same sign as indicated by thesign nibble of the source operand. If an invalid digit or sign code isdetected, a decimal data exception is recognized.

In one embodiment, each of the Convert from Zoned instructions has asame format (an RSL-b format), an example of which is depicted in FIG.4. As depicted in one embodiment, a format 400 of the Convert from Zonedinstruction includes, for instance, the following fields:

Opcode fields 402 a, 402 b: The opcode fields provide an opcode thatindicates the function being performed by the instruction. As examples,one defined opcode defines the function as the long Convert from Zonedinstruction, and another predefined opcode indicates it is an extendedConvert from Zoned instruction.

Length field (L₂) 404: Length field 404 specifies the length (e.g., inbytes) of the second operand. As examples, the length field includes alength code of 0 to 33 for an extended Convert to Zoned instruction, anda length code of 0 to 15 for a long Convert from Zoned instruction.

Base register field (B₂) 406: The base register field designates ageneral register, the contents of which are added to the contents of thedisplacement field to form the second operand address.

Displacement field (D₂) 408: The displacement field includes contentsthat are added to the contents of the general register designated by thebase register field to form the second operand address.

Register field (R₁) 410: The register field designates a register, thecontents of which are the first operand. The register including thefirst operand is sometimes referred to as the first operand location.

Mask field (M₃) 412: The mask field includes, for instance, a sign (S)control (e.g., bit), which in one example is bit 0 of the M₃ field. Whenthis bit is zero, the second operand does not have a sign field and thesign bit of the DFP first operand result is set to 0. When one, thesecond operand is signed. That is, the leftmost four bits of therightmost byte are a sign. The sign bit of the DFP first operand resultis set to zero, when the sign field indicates a positive value; and one,when the sign field indicates a negative value. In one embodiment, bits1 to 3 of the M₃ field are ignored.

During operation of the Convert from Zoned instruction, the secondoperand in the zoned format is converted to the DFP format, and theresult is placed at the first operand location. In one example, thequantum is one and the delivered value is represented with the quantum.The result placed at the first operand location is canonical.

In one embodiment, when an invalid digit or sign code is detected in thesecond operand, a decimal operand data exception is recognized. Aspecification exception is recognized and the operation is suppressedwhen, for instance, any of the following is true: For CDZT, the L₂ fieldis greater than or equal to 16; and for CXZT, the R₁ field designates aninvalid floating point register pair, or the L₂ field is greater than orequal to 34.

In one embodiment, when an ASCII second operand is specified, bit 0 ofthe M₃ field is 0; otherwise a decimal operand data exception isrecognized. That is, a sign value of 0011 binary is not a valid sign.

Further details regarding execution of a Convert from Zoned instructionare described with reference to FIG. 5. In one example, it is theprocessor that executes the Convert from Zoned instruction that performsthis logic.

Initially, a determination is made as to whether the opcode of theConvert from Zoned instruction indicates it is the extended or longformat, INQUIRY 500. That is, is the instruction being executed the longConvert from Zoned instruction or the extended Convert from Zonedinstruction. If the opcode indicates that it is the long Convert fromZoned instruction, then a further determination is made as to whetherthe length field (L₂) provided in the instruction specifies a lengthgreater than 15, INQUIRY 502. If the length field specifies a lengthgreater than 15, then an exception is provided indicating that it ismore than 16 digits (0 to 15), STEP 504.

Returning to INQUIRY 502, if the length field does not specify a lengthgreater than 15, then the source zoned digits (at least a portion of thesecond operand) are read from memory, STEP 506. Thereafter, the sourcezoned digits read from memory are converted to a decimal floating pointformat, STEP 508. In this example, it is converted to a double precisionDFP operand with a zero exponent.

Additionally, a determination is made as to whether the sign control (S)designated in the mask field (M₃) is set to 1, INQUIRY 510. If the signcontrol is not equal to one, then the sign of the DFP number is forcedpositive, STEP 512, and the target floating point register is updatedwith the converted value, including the forced sign, STEP 514.

Returning to INQUIRY 510, if the sign control is equal to 1, then thesource sign field (of the second operand) is read from memory, STEP 516.Thereafter, the sign of the DFP number is set to the sign of the source,STEP 518, and the target floating point register is updated with theconverted value and the sign (e.g., bit 0 of the DFP format), STEP 514.

Returning to INQUIRY 500, if the opcode indicates that it is an extendedConvert from Zoned instruction, then a determination is made as towhether the length field of the instruction specifies a length greaterthan 33, INQUIRY 530. If the length field specifies a length greaterthan 33, then an exception is provided indicating more than 34 digits (0to 33), STEP 532. However, if the length field does not specify a lengthgreater than 33, then a determination is made as to whether the R₁ fieldof the instruction specifies an invalid floating point register pair,INQUIRY 534. If an invalid floating point register pair is indicated,then an exception is provided, STEP 536. Otherwise, the source zoneddigits (at least a portion of the second operand) are read from memory,STEP 538. Thereafter, the source zoned digits read from memory areconverted to a decimal floating point format, STEP 540. In this example,the digits (at least a portion of the second operand) are converted toan extended precision data floating point operation with a zeroexponent.

Thereafter, a determination is made as to whether the sign (S) controlin the mask field of the instruction is set to one, INQUIRY 542. If thesign control is not equal to 1, then the sign of the data floating pointnumber is forced to positive, STEP 544. However, if the sign control isequal to 1, then the source sign field (of the second operand) is readfrom memory, STEP 546, and the sign of the DFP number is set to the signof the source, STEP 548. Subsequent to setting the sign either in STEP544 or STEP 548, the target floating point register pair is updated withthe converted decimal floating point format and the sign, STEP 550.

Referenced above are two steps for converting source zoned digits readfrom memory to a decimal floating point format. In particular, STEP 508converts the source to a double precision decimal floating point operandwith a zero exponent, and STEP 540 converts the source to an extendedprecision data floating point operation with a zero exponent. Furtherdetails regarding the conversions are described below, as well as in theabove-referenced “z/Architecture Principles of Operation,” IBM®Publication No. SA22-7832-08, Ninth Edition, August, 2010, which ishereby incorporated herein by reference in its entirety.

One embodiment of the process of converting from a Zoned formattednumber to the DFP format is as follows: The source digits are read frommemory. The Binary Coded Decimal (BCD) digits in the right 4-bits ofeach byte of source data is padded on the left with zero's, ifnecessary, such that a total of 16 BCD digits exist for a doubleprecision operation, and such that 34 digits exist for an extendedprecision operation. These BCD digits are then converted from BCD toDensely Packed Decimal (DPD) such that every 3 BCD digits starting onthe right of the source data is converted to a 10-bit DPD group for allthe BCD digits except the leftmost BCD digit. Thus, there exist 5 DPDgroups for the double precision conversion and 11 DPD groups for theextended precision conversion. These DPD groups make up bits 14-63 ofthe double precision result and bits 17-127 of an extended precisionresult. Bits 6-13 are the exponent field of a double precision resultand with 2 bits from the combo field in bits 1-5 are set to a value of398 for double precision operations. For extended precision operations,bits 6-17 are exponent field bits and with 2 bits from the combo fieldare set to a value of 6176 for extended precision operations.

If the most significant BCD digit is “8” or “9”, then bits 1 and 2 areset to ‘1’; bits 3 and 4 are the most significant 2 bits of the exponentand so would be set to “01”; and bit 5 is set to ‘0’ for an “8” or ‘1’for a “9”. If the most significant BCD digit is “0” to “7”, then bits 1and 2 are the most significant value of the exponent and so would be setto “01”, and bits 3-5 are set to the rightmost 3 bits of the mostsignificant BCD digit.

The leftmost 4 bits of the rightmost byte of source data is the signcode, if S=1. In this case the result sign bit, bit 0, is set to 1, ifthe value of the sign code is “1011” or “1101”.

Described in detail above are two instructions that provide a means tosignificantly improve traditional storage-to-storage decimal workload.In the traditional storage-to-storage decimal workloads, the EBCDIC orASCII operands are first converted to a packed decimal format, whichstrips out the field codes and puts the numeric digits and sign digitsof two operands in another part of storage. The packed operands are thenoperated on by an arithmetic operation, such as add, subtract, multiplyor divide. These arithmetic operations must wait for the stores of thepack process to complete before they can begin, and these operationsthen store their results to memory. Once the result store is complete,the result is then unpacked back to the target format (EBCDIC or ASCII).The memory dependencies from the operations dominate the performance.

In accordance with an aspect of the present invention, employing the newinstructions (e.g., recompiling the code with the new instructionsenabled) replaces the Pack or PKA instruction with the CDZT or CXZTdepending on the target format. The mathematical operation can then bereplaced with its DFP equivalent (e.g., AD/XTR, SD/XTR, MD/XTR, DT/XTR)such that there is no wait for any operands to be stored or read frommemory. These instructions operate in a similar amount of time as add(AP), subtract (SP), multiply (MP) or divide (DP), but without thememory overhead. The second memory dependency is avoided when the UNPKor UNPKA operation is replaced and the result is directly converted tothe target format via CZDT or CZXT instructions described below.

Traditional storage-to-storage decimal pack operations are able toprocess 15 digits and a sign requiring 3 overlapping pack operations toprocess each 31-digit (and sign) operand typically found inapplications, such as a COBOL applications. Having to break an operandinto smaller overlapping mini-operands adds to the complexity of thecompiler and the compiled code; requires additional instructions to beexecuted to perform a given task, such as handling carry/borrow betweenmini-operands; and impacts performance. Since CXZT is capable ofconverting 34 digits and a sign code into a DFP operand, compilers cantreat the common 31-digit and sign operands (e.g., COBOL operands) as asingle entity, simplifying the compiled code and improving performance.

As described herein, the CDZT and CXZT instructions provide an efficientmeans for converting data from EBCDIC or ASCII in memory directly to theDFP formats in register. They allow the data to be converted from EBCDICor ASCII to the DFP format in a single step. Previously, the processrequired using Pack or PKA operations to convert the data to the packeddecimal format. The data must then be loaded into general purposeregisters (GPRs), but since there is no length-controlled load currentlyin the instruction set architecture, this often requires a mix of word,half-word and byte-load operations. Other instructions, CDSTR or CXSTR,can then be used to convert the packed decimal data in the GPR/GPR-pairto the target DFP format. In accordance with an aspect of the presentinvention, PACK/PKA and CDSTR/CXSTR are replaced by one instruction,CDZT or CXZT.

In addition to Convert from Zoned to decimal floating pointinstructions, in accordance with a further aspect of the presentinvention, Convert to Zoned from decimal floating point instructions areprovided. These instructions provide an efficient means of convertingdata from the decimal floating point format held in a floating pointregister or floating point register pair to EBCDIC or ASCII data andstoring it directly to memory.

For instance, referring to FIG. 6, in one example, a DFP operand in asource register or source register pair is converted to EBCDIC or ASCIIdata, STEP 600. The converted result is then stored in a target memorylocation, STEP 602. These instructions allow the data to be convertedfrom the DFP format directly to EBCDIC and ASCII in a single step.

Examples of these instructions include a long Convert to Zonedinstruction (CZDT) and an extended Convert to Zoned instruction (CZXT).The long Convert to Zoned instruction, CZDT, reads the double precisionDFP operand data from a specified FPR register, converts the mantissa tothe zoned format, and writes it to the target memory location. Likewise,the extended Convert to Zoned instruction, CZXT, reads the extendedprecision DFP operand data from a specified FPR register pair, andconverts the mantissa to a zoned format, and writes it to the targetmemory location. If the length of the memory location specified is notsufficient to fit all of the leftmost non-zero digits of the sourceoperand, a decimal overflow exception is recognized, provided thedecimal overflow mask is enabled. In the event not all the digits fitinto the specified memory location, a specific condition code is set(e.g., 3). The sign of the DFP operand is copied to the sign nibble ofthe result in memory, if the sign field to set. The positive signencoding used is controlled by the P field in the instruction text,described below, and the results of the zero operand can conditionallybe forced positive by the Z field of the instruction text, alsodescribed below. This sort of sign manipulation is commonly required incompiler code and inclusion of this function directly into theinstruction provides a performance savings and simplifies the compilercode.

One embodiment of a format (RSL-b) of a Convert to Zoned instruction isdescribed with reference to FIG. 7. In one example, a format 700 of theConvert to Zoned instruction includes the following fields:

-   -   Opcode fields 702 a, 702 b: The opcode fields provide an opcode        that indicates the function being performed by the instruction.        As examples, one defined opcode specifies the function as the        long Convert to Zoned instruction, and another predefined opcode        indicates it is an extended Convert to Zoned instruction.    -   Length field (L₂) 704: Length field 704 specifies the length        (e.g., in bytes) of the second operand. As examples, the length        field includes a length code of 0 to 33 for an extended Convert        to Zoned instruction, and a length code of 0 to 15 for a long        Convert to Zoned instruction. Further, the number of rightmost        significand digits of the first operand to be converted is        specified by L₂.    -   Base register field (B₂) 706: The base register field designates        a general register, the contents of which are added to the        contents of the displacement field to form the second operand        address.    -   Displacement field (D₂) 708: The displacement field includes        contents that are added to the contents of the general register        designated by the base register field to form the second operand        address.    -   Register field (R₁) 710: The register field designates a        register, the contents of which are the first operand.    -   Mask field (M₃) 712: The mask field includes, for instance:        -   Sign Control (S): Bit 0 of the M₃ field is the sign control.            When S is zero, the second operand does not have a sign            field. When S is one, the second operand has a sign field.            That is, the leftmost four bit positions of the rightmost            byte are a sign.        -   Zone Control (Z): Bit 1 of the M₃ field is the zone control.            When Z is zero, each zone field of the second operand is            stored as 1111 binary.        -   When Z is one, each zone field of the second operand is            stored as 0011 binary.        -   Plus-Sign-Code Control (P): Bit 2 of the M₃ field is the            plus-sign-code control. When P is zero, the plus sign is            encoded as 1100 binary. When P is one, the plus sign is            encoded as 1111 binary. When the S bit is zero, the P bit is            ignored and assumed to be zero.        -   Force-Plus-Zero Control (F): Bit 3 of the M₃ field is the            force-plus-zero control. When F is zero, no action is taken.            When F is one and the absolute value of the result placed at            the second operand location is zero, the sign of the result            is set to indicate a plus value with the sign code specified            by the P bit. When the S bit is zero, the F bit is ignored            and assumed to be zero.

In operation, the specified number of rightmost significand digits ofthe DFP first operand and the sign bit of the first operand areconverted to the zoned format, and the result is placed at the secondoperand location. A right-units view of the first operand with quantumof one is implied. The exponent in the combination field is ignored andtreated as if it had a value of zero, before biasing.

The number of rightmost significand digits of the first operand to beconverted is specified by Lz. The length in bytes of the second operandis 1-34 for CZXT, corresponding to a length code in L₂ of 0 to 33,meaning 1-34 digits. The length in bytes of the second operand is 1-16for CZDT, corresponding to a length code in L₂ of 0 to 15, meaning 1 to16 digits.

In one embodiment, the operation is performed for any first operand,including an infinity, QNaN, or SNaN, without causing an IEEE exception.If the first operand is infinity or a NaN, a zero digit is assumed to bethe leftmost digit of the significand, the specified number of rightmostsignificand digits and the sign bit are converted to the zoned format,the result is placed at the second operand location, and executioncompletes with a specific condition code (e.g., 3).

When leftmost non-zero digits of the result are lost because the secondoperand field is too short, the result is obtained by ignoring theoverflow digits, a specified condition code (e.g., of 3) is set, and ifthe decimal overflow mask bit is one, a program interruption of decimaloverflow occurs. The operand lengths alone are not an indication ofoverflow; non-zero digits are to be lost during the operation.

A specification exception is recognized, and the operation is suppressedwhen, for instance, any of the following is true: for CZDT, the L₂ fieldis greater than or equal to 16, meaning 17 or more digits. For CZXT, theR₁ field designates an invalid floating point register pair, or the L₂field is greater than or equal to 34, meaning 35 or more digits.

Examples of resulting condition codes include:

0 Source is zero 1 Source is less than zero 2 Source is greater thanzero 3 Infinity, QNan, SNaN, partial result.

In one embodiment, an ASCII zoned decimal operand may be stored assigned when the S bit is one. This is up to the program as ASCIIrepresentations are usually unsigned and positive with no concept of arightmost zone being used as a sign. Further, a completion with aparticular condition code (e.g., 0) indicates that the absolute value ofthe first operand is zero.

Relationships among the M₃ control bits versus the first operand DFPsign and the absolute value of the resulting second operand being zeroare illustrated in the below table, which is provided as one example:

M₃ Plus Force Sign- Plus- 1^(st) Result Zone Sign Code Zero Op Abso-Zone Sign Control Control Control Control Sign lute Value Value (Z) (S)(P) (F) Bit Value (Binary) (Binary) 0 0 x x x x 1111 — 1 0 x 0 x 1100 01 x 1101 1 1 zero 1100 1 nonzero 1101 1 0 0 x 1111 1 x 1101 1 0 x 1111 1zero 1111 1 nonzero 1101 1 0 x x x x 0011 — 1 0 x 0 x 1100 0 1 x 1101 11 zero 1100 1 nonzero 1101 1 0 0 x 1111 1 x 1101 1 0 x 1111 1 zero 11111 nonzero 1101 x Ignored — Not applicable

Further details regarding the logic of the Convert to Zoned instructionare described with reference to FIG. 8. In one example, this logic isperformed by a processor executing a Convert to Zoned machineinstruction.

Referring to FIG. 8, initially, a determination is made as to whetherthis is an extended Convert to Zoned instruction or a long Convert toZoned instruction, as indicated by the opcode of the instruction,INQUIRY 800. If it is a long Convert to Zoned instruction, as indicatedby the opcode, then a further determination is made as to whether the L₂field specifies a length greater than 15, INQUIRY 802. If the L₂ fielddoes specify a length greater than 15, then an exception is providedsince there are more than 16 digits (0-15), STEP 804.

Returning to INQUIRY 802, if the length field does not specify a lengthgreater than 15, then the DFP operand is read from the floating pointregister designated in the convert instruction (using R₁), STEP 806. Thesource DFP digits of the read DFP operand are then converted to BCDdigits, STEP 808.

Subsequent to the conversion, a determination is made as whethernon-zero digits fit in the length specified by L₂, INQUIRY 810. Ifnon-zero digits do not fit, then an overflow exception is indicated,STEP 812. Otherwise, a further determination is made as to whether the Zbit of the mask field is equal to 1, INQUIRY 814. If Z is equal to 1,then the zone field and sign codes are set to “0011”, STEP 816.Otherwise, the zone field and sign codes are set to “1111”, STEP 818.

Subsequent to setting the zone field and sign codes, a furtherdetermination is made as to whether the S bit of the mask field is setto 1, INQUIRY 820. If the S bit is not set to 1, then the BCD digits,sign field and field codes are stored to memory in the proper format,STEP 822. One example of a zoned format is as follows:

In this example, the rightmost four bits of a byte are called thenumeric bits (N) and normally include a code representing a decimaldigit. The leftmost four bits of a byte are called the zone bits (Z),except for the rightmost byte of a decimal operand, where these bits maybe treated either as a zone or as a sign (S).

Returning to INQUIRY 820, if the S bit is equal to 1, then a furtherdetermination is made as to whether the Z bit in the mask is set to 1,INQUIRY 824. If Z is equal to 1, then a determination is made as towhether the result is equal to zero, STEP 826. If the result is equal tozero, then the result sign is set to positive, STEP 828. If the resultis not set to equal to zero or Z is not equal to one, then the resultsign is set to the DFP sign, STEP 830.

Subsequent to setting the result sign, a determination is made as towhether the result sign is positive, INQUIRY 832. If the result sign isnot positive, then processing continues with STEP 822, storing the BCDdigits, sign field and field codes to memory in the proper format.However, if the result sign is positive, INQUIRY 832, a furtherdetermination is made as to whether the P bit of the mask field is setto 1, INQUIRY 834. If the P bit is set to one, then the sign is setequal to 1111; otherwise, the sign is set equal to 1100, STEP 838. Aftersetting the sign, processing continues with STEP 822.

Returning to INQUIRY 800, if this is an extended Convert to Zonedinstruction, then a determination is made as to whether the length fieldspecifies a length greater than 33, INQUIRY 850. If the length fieldspecifies a length greater than 33, then an exception is specifiedindicating more than 34 digits, STEP 852. Otherwise, a determination ismade as to whether the register field (R₁) specifies an invalid floatingpoint register pair, INQUIRY 854. If not, then processing continues withSTEP 806. Otherwise, an exception is provided, STEP 856. This completesthe description of embodiments of the Convert to Zoned instruction.

Referenced above is a step for converting source DFP digits to BCDdigits. Further details regarding the conversion are described below, aswell as in the above-referenced “z/Architecture Principles ofOperation,” IBM® Publication No. SA22-7832-08, Ninth Edition, August,2010, which is hereby incorporated herein by reference in its entirety.The below description also provides details regarding the process ofconverting from DFP to zoned format

In one example, for the double precision format, the most significantdigit of the mantissa data to be converted to zoned format is containedin the combo field, which is bits 1-5 of the source data. Bit 0 is thesign bit, with a negative value being indicated with bit 0 being a ‘1’.Bits 6-13 are the exponent continuation field and are ignored by thisoperation. Bits 14-63 are the Encoded Trailing Significand and containthe remaining 15 digits of decimal data and are encoded in the DPD(densely packed decimal) format.

For the extended precision format, in one example, the most significantdigit of the mantissa data to be converted to zoned format is containedin the combo field, which is bits 1-5 of the source data. Bit 0 is thesign bit, with a negative value being indicated with bit 0 being a ‘1’.Bits 6-17 are the exponent continuation field and are ignored by thisoperation. Bits 18-127 are the Encoded Trailing Significand and containthe remaining 33 digits of decimal data that are encoded in the DPDformat,

For both the double precision and extended precision formats, thetrailing significand digits that are DPD encoded digits are convertedfrom DPD format to BCD (binary coded decimal) format and the digit fromthe combo field (bits 1-5) is pre-pended to the beginning of thosedigits. The DPD to BCD conversion requires only a few gates, and throughsuch gates, blocks of 10-bit DPD data is decompressed into blocks of12-bit BCD data, such that each BCD block includes three 4-bit BCDnumbers. The string of numbers is checked for leading zeros and is thencompared to the L₂ field of the instruction to determine if an overflowsituation occurs, and if it does, it zeros out the appropriate mostsignificant digits (those being the digits that will not fit into thespecified memory length (specified by L₂) once the data is expanded tozoned decimal format.

Next 4-bit Zone fields are inserted to the left of each BCD digit suchthat each byte (8-bits) now includes a 4-bit zone field followed by a4-bit BCD digit. Each zone field is either “0011” or “1111” depending onwhether the Z bit in the text is a 0 or a 1. Next, the sign bit from theDFP source operand is used to determine a sign code if S=1 in theinstruction. If the BCD digits are all 0 and F=1, then the sign isignored and a positive sign code created. Otherwise, the sign codegenerated is the sign of the DFP source operand from bit 0 and anegative sign is encoded as a “1101”; a positive sign is encoded as a“1100” if P=0 or as a “1111” if P=1. This sign code then replaces thefield code to the left of the least significant BCD digit. (In oneembodiment, the sign is processed in parallel to the field codes and isinserted to the left of the least significant BCD digit, instead of thefield code.) This result is then written to memory.

Described in detail above are two machine instructions, CZDT and CZXTthat convert a decimal floating point operand in a source floating pointregister or register pair to EBCDIC or ASCII data and store it to atarget memory location. These instructions provide a means tosignificantly improve traditional storage-to-storage decimal workloads.Traditional storage-to-storage decimal unpack operations are able toprocess 15 digits and a sign requiring three overlapping unpackoperations to process a 31-digit (and sign) result typically found inapplications, such as COBOL applications. Having to break a result intosmaller overlapping mini-results adds to the complexity of the compilerand impacts performance as it requires additional instructions to beexecuted to perform a given task. Since CZXT is capable of converting aDFP operand containing up to 34 digits and a sign code and storing it tomemory in a single instruction, compilers can treat the common 31-digitand sign results (e.g., COBOL results) as a single entity, simplifyingthe compiled code and improving performance.

Previously, the process required using CSDTR or CSXTR to convert thedata from the DFP format to the packed decimal format in GPRs. The datamust then be stored out of GPRs to memory, but since there is no lengthcontrolled store currently in the instruction set architecture, thisoften required a mix of word, half-word, and byte store operations.Finally, an unpack or UNPKA operation is needed to convert the data inmemory back to EBCDIC or ASCII. These new instructions allow the data tobe converted from the DFP format directly to EBCDIC and ASCII in asingle step. The CZDT or CZXT instruction replaces both the CSDTR/CSXTRand UNPK/UNPKA instructions.

As will be appreciated by one skilled in the art, one or more aspects ofthe present invention may be embodied as a system, method or computerprogram product. Accordingly, one or more aspects of the presentinvention may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system”. Furthermore, one or more aspects of the presentinvention may take the form of a computer program product embodied inone or more computer readable medium(s) having computer readable programcode embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, electromagnetic,infrared or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flashmemory), an optical fiber, a portable compact disc read-only memory(CD-ROM), an optical storage device, a magnetic storage device, or anysuitable combination of the foregoing. In the context of this document,a computer readable storage medium may be any tangible medium that cancontain or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

Referring now to FIG. 9, in one example, a computer program product 900includes, for instance, one or more non-transitory computer readablestorage media 902 to store computer readable program code means or logic904 thereon to provide and facilitate one or more aspects of the presentinvention.

Program code embodied on a computer readable medium may be transmittedusing an appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for one or moreaspects of the present invention may be written in any combination ofone or more programming languages, including an object orientedprogramming language, such as Java, Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language, assembler or similar programming languages. Theprogram code may execute entirely on the user's computer, partly on theuser's computer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

One or more aspects of the present invention are described herein withreference to flowchart illustrations and/or block diagrams of methods,apparatus (systems) and computer program products according toembodiments of the invention. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of one or more aspects of the present invention. In thisregard, each block in the flowchart or block diagrams may represent amodule, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In addition to the above, one or more aspects of the present inventionmay be provided, offered, deployed, managed, serviced, etc. by a serviceprovider who offers management of customer environments. For instance,the service provider can create, maintain, support, etc. computer codeand/or a computer infrastructure that performs one or more aspects ofthe present invention for one or more customers. In return, the serviceprovider may receive payment from the customer under a subscriptionand/or fee agreement, as examples. Additionally or alternatively, theservice provider may receive payment from the sale of advertisingcontent to one or more third parties.

In one aspect of the present invention, an application may be deployedfor performing one or more aspects of the present invention. As oneexample, the deploying of an application comprises providing computerinfrastructure operable to perform one or more aspects of the presentinvention.

As a further aspect of the present invention, a computing infrastructuremay be deployed comprising integrating computer readable code into acomputing system, in which the code in combination with the computingsystem is capable of performing one or more aspects of the presentinvention.

As yet a further aspect of the present invention, a process forintegrating computing infrastructure comprising integrating computerreadable code into a computer system may be provided. The computersystem comprises a computer readable medium, in which the computermedium comprises one or more aspects of the present invention. The codein combination with the computer system is capable of performing one ormore aspects of the present invention.

Although various embodiments are described above, these are onlyexamples. For example, computing environments of other architectures canincorporate and use one or more aspects of the present invention.Further, although certain fields and/or bits are described, others maybe used as well. Additionally, some steps of the flow diagrams may beperformed in parallel or in a differing order. Many changes and/oradditions may be made without departing from the spirit of the presentinvention.

Further, other types of computing environments can benefit from one ormore aspects of the present invention. As an example, a data processingsystem suitable for storing and/or executing program code is usable thatincludes at least two processors coupled directly or indirectly tomemory elements through a system bus. The memory elements include, forinstance, local memory employed during actual execution of the programcode, bulk storage, and cache memory which provide temporary storage ofat least some program code in order to reduce the number of times codemust be retrieved from bulk storage during execution.

Input/Output or I/O devices (including, but not limited to, keyboards,displays, pointing devices, DASD, tape, CDs, DVDs, thumb drives andother memory media, etc.) can be coupled to the system either directlyor through intervening I/O controllers. Network adapters may also becoupled to the system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems, and Ethernet cards are just a few of the available types ofnetwork adapters.

Other examples of computing environments that may incorporate and/or useone or more aspects of the present invention are described below.

Referring to FIG. 10, representative components of a Host Computersystem 5000 to implement one or more aspects of the present inventionare portrayed. The representative host computer 5000 comprises one ormore CPUs 5001 in communication with computer memory (i.e., centralstorage) 5002, as well as I/O interfaces to storage media devices 5011and networks 5010 for communicating with other computers or SANs and thelike. The CPU 5001 is compliant with an architecture having anarchitected instruction set and architected functionality. The CPU 5001may have dynamic address translation (DAT) 5003 for transforming programaddresses (virtual addresses) into real addresses of memory. A DATtypically includes a translation lookaside buffer (TLB) 5007 for cachingtranslations so that later accesses to the block of computer memory 5002do not require the delay of address translation. Typically, a cache 5009is employed between computer memory 5002 and the processor 5001. Thecache 5009 may be hierarchical having a large cache available to morethan one CPU and smaller, faster (lower level) caches between the largecache and each CPU. In some implementations, the lower level caches aresplit to provide separate low level caches for instruction fetching anddata accesses. In one embodiment, an instruction is fetched from memory5002 by an instruction fetch unit 5004 via a cache 5009. The instructionis decoded in an instruction decode unit 5006 and dispatched (with otherinstructions in some embodiments) to instruction execution unit or units5008. Typically several execution units 5008 are employed, for examplean arithmetic execution unit, a floating point execution unit and abranch instruction execution unit. The instruction is executed by theexecution unit, accessing operands from instruction specified registersor memory as needed. If an operand is to be accessed (loaded or stored)from memory 5002, a load/store unit 5005 typically handles the accessunder control of the instruction being executed. Instructions may beexecuted in hardware circuits or in internal microcode (firmware) or bya combination of both.

As noted, a computer system includes information in local (or main)storage, as well as addressing, protection, and reference and changerecording. Some aspects of addressing include the format of addresses,the concept of address spaces, the various types of addresses, and themanner in which one type of address is translated to another type ofaddress. Some of main storage includes permanently assigned storagelocations. Main storage provides the system with directly addressablefast-access storage of data. Both data and programs are to be loadedinto main storage (from input devices) before they can be processed.

Main storage may include one or more smaller, faster-access bufferstorages, sometimes called caches. A cache is typically physicallyassociated with a CPU or an I/O processor. The effects, except onperformance, of the physical construction and use of distinct storagemedia are generally not observable by the program.

Separate caches may be maintained for instructions and for dataoperands. Information within a cache is maintained in contiguous byteson an integral boundary called a cache block or cache line (or line, forshort). A model may provide an EXTRACT CACHE ATTRIBUTE instruction whichreturns the size of a cache line in bytes. A model may also providePREFETCH DATA and PREFETCH DATA RELATIVE LONG instructions which effectsthe prefetching of storage into the data or instruction cache or thereleasing of data from the cache.

Storage is viewed as a long horizontal string of bits. For mostoperations, accesses to storage proceed in a left-to-right sequence. Thestring of bits is subdivided into units of eight bits. An eight-bit unitis called a byte, which is the basic building block of all informationformats. Each byte location in storage is identified by a uniquenonnegative integer, which is the address of that byte location or,simply, the byte address. Adjacent byte locations have consecutiveaddresses, starting with 0 on the left and proceeding in a left-to-rightsequence. Addresses are unsigned binary integers and are 24, 31, or 64bits.

Information is transmitted between storage and a CPU or a channelsubsystem one byte, or a group of bytes, at a time. Unless otherwisespecified, in, for instance, the z/Architecture®, a group of bytes instorage is addressed by the leftmost byte of the group. The number ofbytes in the group is either implied or explicitly specified by theoperation to be performed. When used in a CPU operation, a group ofbytes is called a field. Within each group of bytes, in, for instance,the z/Architecture®, bits are numbered in a left-to-right sequence. Inthe z/Architecture®, the leftmost bits are sometimes referred to as the“high-order” bits and the rightmost bits as the “low-order” bits. Bitnumbers are not storage addresses, however. Only bytes can be addressed.To operate on individual bits of a byte in storage, the entire byte isaccessed. The bits in a byte are numbered 0 through 7, from left toright (in, e.g., the z/Architecture®). The bits in an address may benumbered 8-31 or 40-63 for 24-bit addresses, or 1-31 or 33-63 for 31-bitaddresses; they are numbered 0-63 for 64-bit addresses. Within any otherfixed-length format of multiple bytes, the bits making up the format areconsecutively numbered starting from 0. For purposes of error detection,and in preferably for correction, one or more check bits may betransmitted with each byte or with a group of bytes. Such check bits aregenerated automatically by the machine and cannot be directly controlledby the program. Storage capacities are expressed in number of bytes.When the length of a storage-operand field is implied by the operationcode of an instruction, the field is said to have a fixed length, whichcan be one, two, four, eight, or sixteen bytes. Larger fields may beimplied for some instructions. When the length of a storage-operandfield is not implied but is stated explicitly, the field is said to havea variable length. Variable-length operands can vary in length byincrements of one byte (or with some instructions, in multiples of twobytes or other multiples). When information is placed in storage, thecontents of only those byte locations are replaced that are included inthe designated field, even though the width of the physical path tostorage may be greater than the length of the field being stored.

Certain units of information are to be on an integral boundary instorage. A boundary is called integral for a unit of information whenits storage address is a multiple of the length of the unit in bytes.Special names are given to fields of 2, 4, 8, and 16 bytes on anintegral boundary. A halfword is a group of two consecutive bytes on atwo-byte boundary and is the basic building block of instructions. Aword is a group of four consecutive bytes on a four-byte boundary. Adoubleword is a group of eight consecutive bytes on an eight-byteboundary. A quadword is a group of 16 consecutive bytes on a 16-byteboundary. When storage addresses designate halfwords, words,doublewords, and quadwords, the binary representation of the addresscontains one, two, three, or four rightmost zero bits, respectively.Instructions are to be on two-byte integral boundaries. The storageoperands of most instructions do not have boundary-alignmentrequirements.

On devices that implement separate caches for instructions and dataoperands, a significant delay may be experienced if the program storesinto a cache line from which instructions are subsequently fetched,regardless of whether the store alters the instructions that aresubsequently fetched.

In one embodiment, the invention may be practiced by software (sometimesreferred to licensed internal code, firmware, micro-code, milli-code,pico-code and the like, any of which would be consistent with one ormore aspects the present invention). Referring to FIG. 10, softwareprogram code which embodies one or more aspects of the present inventionmay be accessed by processor 5001 of the host system 5000 from long-termstorage media devices 5011, such as a CD-ROM drive, tape drive or harddrive. The software program code may be embodied on any of a variety ofknown media for use with a data processing system, such as a diskette,hard drive, or CD-ROM. The code may be distributed on such media, or maybe distributed to users from computer memory 5002 or storage of onecomputer system over a network 5010 to other computer systems for use byusers of such other systems.

The software program code includes an operating system which controlsthe function and interaction of the various computer components and oneor more application programs. Program code is normally paged fromstorage media device 5011 to the relatively higher-speed computerstorage 5002 where it is available for processing by processor 5001. Thetechniques and methods for embodying software program code in memory, onphysical media, and/or distributing software code via networks are wellknown and will not be further discussed herein. Program code, whencreated and stored on a tangible medium (including but not limited toelectronic memory modules (RAM), flash memory, Compact Discs (CDs),DVDs, Magnetic Tape and the like is often referred to as a “computerprogram product”. The computer program product medium is typicallyreadable by a processing circuit preferably in a computer system forexecution by the processing circuit.

FIG. 11 illustrates a representative workstation or server hardwaresystem in which one or more aspects of the present invention may bepracticed. The system 5020 of FIG. 11 comprises a representative basecomputer system 5021, such as a personal computer, a workstation or aserver, including optional peripheral devices. The base computer system5021 includes one or more processors 5026 and a bus employed to connectand enable communication between the processor(s) 5026 and the othercomponents of the system 5021 in accordance with known techniques. Thebus connects the processor 5026 to memory 5025 and long-term storage5027 which can include a hard drive (including any of magnetic media,CD, DVD and Flash Memory for example) or a tape drive for example. Thesystem 5021 might also include a user interface adapter, which connectsthe microprocessor 5026 via the bus to one or more interface devices,such as a keyboard 5024, a mouse 5023, a printer/scanner 5030 and/orother interface devices, which can be any user interface device, such asa touch sensitive screen, digitized entry pad, etc. The bus alsoconnects a display device 5022, such as an LCD screen or monitor, to themicroprocessor 5026 via a display adapter.

The system 5021 may communicate with other computers or networks ofcomputers by way of a network adapter capable of communicating 5028 witha network 5029. Example network adapters are communications channels,token ring, Ethernet or modems. Alternatively, the system 5021 maycommunicate using a wireless interface, such as a CDPD (cellular digitalpacket data) card. The system 5021 may be associated with such othercomputers in a Local Area Network (LAN) or a Wide Area Network (WAN), orthe system 5021 can be a client in a client/server arrangement withanother computer, etc. All of these configurations, as well as theappropriate communications hardware and software, are known in the art.

FIG. 12 illustrates a data processing network 5040 in which one or moreaspects of the present invention may be practiced. The data processingnetwork 5040 may include a plurality of individual networks, such as awireless network and a wired network, each of which may include aplurality of individual workstations 5041, 5042, 5043, 5044.Additionally, as those skilled in the art will appreciate, one or moreLANs may be included, where a LAN may comprise a plurality ofintelligent workstations coupled to a host processor.

Still referring to FIG. 12, the networks may also include mainframecomputers or servers, such as a gateway computer (client server 5046) orapplication server (remote server 5048 which may access a datarepository and may also be accessed directly from a workstation 5045). Agateway computer 5046 serves as a point of entry into each individualnetwork. A gateway is needed when connecting one networking protocol toanother. The gateway 5046 may be preferably coupled to another network(the Internet 5047 for example) by means of a communications link. Thegateway 5046 may also be directly coupled to one or more workstations5041, 5042, 5043, 5044 using a communications link. The gateway computermay be implemented utilizing an IBM eServer™ System z® server availablefrom International Business Machines Corporation.

Referring concurrently to FIG. 11 and FIG. 12, software programming codewhich may embody one or more aspects of the present invention may beaccessed by the processor 5026 of the system 5020 from long-term storagemedia 5027, such as a CD-ROM drive or hard drive. The softwareprogramming code may be embodied on any of a variety of known media foruse with a data processing system, such as a diskette, hard drive, orCD-ROM. The code may be distributed on such media, or may be distributedto users 5050, 5051 from the memory or storage of one computer systemover a network to other computer systems for use by users of such othersystems.

Alternatively, the programming code may be embodied in the memory 5025,and accessed by the processor 5026 using the processor bus. Suchprogramming code includes an operating system which controls thefunction and interaction of the various computer components and one ormore application programs 5032. Program code is normally paged fromstorage media 5027 to high-speed memory 5025 where it is available forprocessing by the processor 5026. The techniques and methods forembodying software programming code in memory, on physical media, and/ordistributing software code via networks are well known and will not befurther discussed herein. Program code, when created and stored on atangible medium (including but not limited to electronic memory modules(RAM), flash memory, Compact Discs (CDs), DVDs, Magnetic Tape and thelike is often referred to as a “computer program product”. The computerprogram product medium is typically readable by a processing circuitpreferably in a computer system for execution by the processing circuit.

The cache that is most readily available to the processor (normallyfaster and smaller than other caches of the processor) is the lowest (L₁or level one) cache and main store (main memory) is the highest levelcache (L₃ if there are 3 levels). The lowest level cache is oftendivided into an instruction cache (I-Cache) holding machine instructionsto be executed and a data cache (D-Cache) holding data operands.

Referring to FIG. 13, an exemplary processor embodiment is depicted forprocessor 5026. Typically one or more levels of cache 5053 are employedto buffer memory blocks in order to improve processor performance. Thecache 5053 is a high speed buffer holding cache lines of memory datathat are likely to be used. Typical cache lines are 64, 128 or 256 bytesof memory data. Separate caches are often employed for cachinginstructions than for caching data. Cache coherence (synchronization ofcopies of lines in memory and the caches) is often provided by various“snoop” algorithms well known in the art. Main memory storage 5025 of aprocessor system is often referred to as a cache. In a processor systemhaving 4 levels of cache 5053, main storage 5025 is sometimes referredto as the level 5 (L5) cache since it is typically faster and only holdsa portion of the non-volatile storage (DASD, tape etc) that is availableto a computer system. Main storage 5025 “caches” pages of data paged inand out of the main storage 5025 by the operating system.

A program counter (instruction counter) 5061 keeps track of the addressof the current instruction to be executed. A program counter in az/Architecture® processor is 64 bits and can be truncated to 31 or 24bits to support prior addressing limits. A program counter is typicallyembodied in a PSW (program status word) of a computer such that itpersists during context switching. Thus, a program in progress, having aprogram counter value, may be interrupted by, for example, the operatingsystem (context switch from the program environment to the operatingsystem environment). The PSW of the program maintains the programcounter value while the program is not active, and the program counter(in the PSW) of the operating system is used while the operating systemis executing. Typically, the program counter is incremented by an amountequal to the number of bytes of the current instruction. RISC (ReducedInstruction Set Computing) instructions are typically fixed length whileCISC (Complex Instruction Set Computing) instructions are typicallyvariable length. Instructions of the IBM z/Architecture® are CISCinstructions having a length of 2, 4 or 6 bytes. The Program counter5061 is modified by either a context switch operation or a branch takenoperation of a branch instruction for example. In a context switchoperation, the current program counter value is saved in the programstatus word along with other state information about the program beingexecuted (such as condition codes), and a new program counter value isloaded pointing to an instruction of a new program module to beexecuted. A branch taken operation is performed in order to permit theprogram to make decisions or loop within the program by loading theresult of the branch instruction into the program counter 5061.

Typically an instruction fetch unit 5055 is employed to fetchinstructions on behalf of the processor 5026. The fetch unit eitherfetches “next sequential instructions”, target instructions of branchtaken instructions, or first instructions of a program following acontext switch. Modern Instruction fetch units often employ prefetchtechniques to speculatively prefetch instructions based on thelikelihood that the prefetched instructions might be used. For example,a fetch unit may fetch 16 bytes of instruction that includes the nextsequential instruction and additional bytes of further sequentialinstructions.

The fetched instructions are then executed by the processor 5026. In anembodiment, the fetched instruction(s) are passed to a dispatch unit5056 of the fetch unit. The dispatch unit decodes the instruction(s) andforwards information about the decoded instruction(s) to appropriateunits 5057, 5058, 5060. An execution unit 5057 will typically receiveinformation about decoded arithmetic instructions from the instructionfetch unit 5055 and will perform arithmetic operations on operandsaccording to the opcode of the instruction. Operands are provided to theexecution unit 5057 preferably either from memory 5025, architectedregisters 5059 or from an immediate field of the instruction beingexecuted. Results of the execution, when stored, are stored either inmemory 5025, registers 5059 or in other machine hardware (such ascontrol registers, PSW registers and the like).

A processor 5026 typically has one or more units 5057, 5058, 5060 forexecuting the function of the instruction. Referring to FIG. 14A, anexecution unit 5057 may communicate with architected general registers5059, a decode/dispatch unit 5056, a load store unit 5060, and other5065 processor units by way of interfacing logic 5071. An execution unit5057 may employ several register circuits 5067, 5068, 5069 to holdinformation that the arithmetic logic unit (ALU) 5066 will operate on.The ALU performs arithmetic operations such as add, subtract, multiplyand divide as well as logical function such as and, or and exclusive-or(XOR), rotate and shift. Preferably the ALU supports specializedoperations that are design dependent. Other circuits may provide otherarchitected facilities 5072 including condition codes and recoverysupport logic for example. Typically the result of an ALU operation isheld in an output register circuit 5070 which can forward the result toa variety of other processing functions. There are many arrangements ofprocessor units, the present description is only intended to provide arepresentative understanding of one embodiment.

An ADD instruction for example would be executed in an execution unit5057 having arithmetic and logical functionality while a floating pointinstruction for example would be executed in a floating point executionhaving specialized floating point capability. Preferably, an executionunit operates on operands identified by an instruction by performing anopcode defined function on the operands. For example, an ADD instructionmay be executed by an execution unit 5057 on operands found in tworegisters 5059 identified by register fields of the instruction.

The execution unit 5057 performs the arithmetic addition on two operandsand stores the result in a third operand where the third operand may bea third register or one of the two source registers. The execution unitpreferably utilizes an Arithmetic Logic Unit (ALU) 5066 that is capableof performing a variety of logical functions such as Shift, Rotate, And,Or and XOR as well as a variety of algebraic functions including any ofadd, subtract, multiply, divide. Some ALUs 5066 are designed for scalaroperations and some for floating point. Data may be Big Endian (wherethe least significant byte is at the highest byte address) or LittleEndian (where the least significant byte is at the lowest byte address)depending on architecture. The IBM z/Architecture® is Big Endian. Signedfields may be sign and magnitude, 1's complement or 2's complementdepending on architecture. A 2's complement number is advantageous inthat the ALU does not need to design a subtract capability since eithera negative value or a positive value in 2's complement requires only anaddition within the ALU. Numbers are commonly described in shorthand,where a 12 bit field defines an address of a 4,096 byte block and iscommonly described as a 4 Kbyte (Kilo-byte) block, for example.

Referring to FIG. 14B, branch instruction information for executing abranch instruction is typically sent to a branch unit 5058 which oftenemploys a branch prediction algorithm such as a branch history table5082 to predict the outcome of the branch before other conditionaloperations are complete. The target of the current branch instructionwill be fetched and speculatively executed before the conditionaloperations are complete. When the conditional operations are completedthe speculatively executed branch instructions are either completed ordiscarded based on the conditions of the conditional operation and thespeculated outcome. A typical branch instruction may test conditioncodes and branch to a target address if the condition codes meet thebranch requirement of the branch instruction, a target address may becalculated based on several numbers including ones found in registerfields or an immediate field of the instruction for example. The branchunit 5058 may employ an ALU 5074 having a plurality of input registercircuits 5075, 5076, 5077 and an output register circuit 5080. Thebranch unit 5058 may communicate with general registers 5059, decodedispatch unit 5056 or other circuits 5073, for example.

The execution of a group of instructions can be interrupted for avariety of reasons including a context switch initiated by an operatingsystem, a program exception or error causing a context switch, an I/Ointerruption signal causing a context switch or multi-threading activityof a plurality of programs (in a multi-threaded environment), forexample. Preferably a context switch action saves state informationabout a currently executing program and then loads state informationabout another program being invoked. State information may be saved inhardware registers or in memory for example. State informationpreferably comprises a program counter value pointing to a nextinstruction to be executed, condition codes, memory translationinformation and architected register content. A context switch activitycan be exercised by hardware circuits, application programs, operatingsystem programs or firmware code (microcode, pico-code or licensedinternal code (LIC)) alone or in combination.

A processor accesses operands according to instruction defined methods.The instruction may provide an immediate operand using the value of aportion of the instruction, may provide one or more register fieldsexplicitly pointing to either general purpose registers or specialpurpose registers (floating point registers for example). Theinstruction may utilize implied registers identified by an opcode fieldas operands. The instruction may utilize memory locations for operands.A memory location of an operand may be provided by a register, animmediate field, or a combination of registers and immediate field asexemplified by the z/Architecture® long displacement facility whereinthe instruction defines a base register, an index register and animmediate field (displacement field) that are added together to providethe address of the operand in memory for example. Location hereintypically implies a location in main memory (main storage) unlessotherwise indicated.

Referring to FIG. 14C, a processor accesses storage using a load/storeunit 5060. The load/store unit 5060 may perform a load operation byobtaining the address of the target operand in memory 5053 and loadingthe operand in a register 5059 or another memory 5053 location, or mayperform a store operation by obtaining the address of the target operandin memory 5053 and storing data obtained from a register 5059 or anothermemory 5053 location in the target operand location in memory 5053. Theload/store unit 5060 may be speculative and may access memory in asequence that is out-of-order relative to instruction sequence, howeverthe load/store unit 5060 is to maintain the appearance to programs thatinstructions were executed in order. A load/store unit 5060 maycommunicate with general registers 5059, decode/dispatch unit 5056,cache/memory interface 5053 or other elements 5083 and comprises variousregister circuits, ALUs 5085 and control logic 5090 to calculate storageaddresses and to provide pipeline sequencing to keep operationsin-order. Some operations may be out of order but the load/store unitprovides functionality to make the out of order operations to appear tothe program as having been performed in order, as is well known in theart.

Preferably addresses that an application program “sees” are oftenreferred to as virtual addresses. Virtual addresses are sometimesreferred to as “logical addresses” and “effective addresses”. Thesevirtual addresses are virtual in that they are redirected to physicalmemory location by one of a variety of dynamic address translation (DAT)technologies including, but not limited to, simply prefixing a virtualaddress with an offset value, translating the virtual address via one ormore translation tables, the translation tables preferably comprising atleast a segment table and a page table alone or in combination,preferably, the segment table having an entry pointing to the pagetable. In the z/Architecture®, a hierarchy of translation is providedincluding a region first table, a region second table, a region thirdtable, a segment table and an optional page table. The performance ofthe address translation is often improved by utilizing a translationlookaside buffer (TLB) which comprises entries mapping a virtual addressto an associated physical memory location. The entries are created whenthe DAT translates a virtual address using the translation tables.Subsequent use of the virtual address can then utilize the entry of thefast TLB rather than the slow sequential translation table accesses. TLBcontent may be managed by a variety of replacement algorithms includingLRU (Least Recently used).

In the case where the processor is a processor of a multi-processorsystem, each processor has responsibility to keep shared resources, suchas I/O, caches, TLBs and memory, interlocked for coherency. Typically,“snoop” technologies will be utilized in maintaining cache coherency. Ina snoop environment, each cache line may be marked as being in any oneof a shared state, an exclusive state, a changed state, an invalid stateand the like in order to facilitate sharing.

I/O units 5054 (FIG. 13) provide the processor with means for attachingto peripheral devices including tape, disc, printers, displays, andnetworks for example. I/O units are often presented to the computerprogram by software drivers. In mainframes, such as the System z® fromIBM®, channel adapters and open system adapters are I/O units of themainframe that provide the communications between the operating systemand peripheral devices.

Further, other types of computing environments can benefit from one ormore aspects of the present invention. As an example, as mentionedherein, an environment may include an emulator (e.g., software or otheremulation mechanisms), in which a particular architecture (including,for instance, instruction execution, architected functions, such asaddress translation, and architected registers) or a subset thereof isemulated (e.g., on a native computer system having a processor andmemory). In such an environment, one or more emulation functions of theemulator can implement one or more aspects of the present invention,even though a computer executing the emulator may have a differentarchitecture than the capabilities being emulated. As one example, inemulation mode, the specific instruction or operation being emulated isdecoded, and an appropriate emulation function is built to implement theindividual instruction or operation.

In an emulation environment, a host computer includes, for instance, amemory to store instructions and data; an instruction fetch unit tofetch instructions from memory and to optionally, provide localbuffering for the fetched instruction; an instruction decode unit toreceive the fetched instructions and to determine the type ofinstructions that have been fetched; and an instruction execution unitto execute the instructions. Execution may include loading data into aregister from memory; storing data back to memory from a register; orperforming some type of arithmetic or logical operation, as determinedby the decode unit. In one example, each unit is implemented insoftware. For instance, the operations being performed by the units areimplemented as one or more subroutines within emulator software.

More particularly, in a mainframe, architected machine instructions areused by programmers, usually today “C” programmers, often by way of acompiler application. These instructions stored in the storage mediummay be executed natively in a z/Architecture® IBM® Server, oralternatively in machines executing other architectures. They can beemulated in the existing and in future IBM® mainframe servers and onother machines of IBM® (e.g., Power Systems servers and System x®Servers). They can be executed in machines running Linux on a widevariety of machines using hardware manufactured by IBM®, AMD®, andothers. Besides execution on that hardware under a z/Architecture®,Linux can be used as well as machines which use emulation by Hercules,UMX, or FSI (Fundamental Software, Inc), where generally execution is inan emulation mode. In emulation mode, emulation software is executed bya native processor to emulate the architecture of an emulated processor.

The native processor typically executes emulation software comprisingeither firmware or a native operating system to perform emulation of theemulated processor. The emulation software is responsible for fetchingand executing instructions of the emulated processor architecture. Theemulation software maintains an emulated program counter to keep trackof instruction boundaries. The emulation software may fetch one or moreemulated machine instructions at a time and convert the one or moreemulated machine instructions to a corresponding group of native machineinstructions for execution by the native processor. These convertedinstructions may be cached such that a faster conversion can beaccomplished. Notwithstanding, the emulation software is to maintain thearchitecture rules of the emulated processor architecture so as toassure operating systems and applications written for the emulatedprocessor operate correctly. Furthermore, the emulation software is toprovide resources identified by the emulated processor architectureincluding, but not limited to, control registers, general purposeregisters, floating point registers, dynamic address translationfunction including segment tables and page tables for example, interruptmechanisms, context switch mechanisms, Time of Day (TOD) clocks andarchitected interfaces to I/O subsystems such that an operating systemor an application program designed to run on the emulated processor, canbe run on the native processor having the emulation software.

A specific instruction being emulated is decoded, and a subroutine iscalled to perform the function of the individual instruction. Anemulation software function emulating a function of an emulatedprocessor is implemented, for example, in a “C” subroutine or driver, orsome other method of providing a driver for the specific hardware aswill be within the skill of those in the art after understanding thedescription of the preferred embodiment. Various software and hardwareemulation patents including, but not limited to U.S. Pat. No. 5,551,013,entitled “Multiprocessor for Hardware Emulation”, by Beausoleil et al.;and U.S. Pat. No. 6,009,261, entitled “Preprocessing of Stored TargetRoutines for Emulating Incompatible Instructions on a Target Processor”,by Scalzi et al; and U.S. Pat. No. 5,574,873, entitled “Decoding GuestInstruction to Directly Access Emulation Routines that Emulate the GuestInstructions”, by Davidian et al; and U.S. Pat. No. 6,308,255, entitled“Symmetrical Multiprocessing Bus and Chipset Used for CoprocessorSupport Allowing Non-Native Code to Run in a System”, by Gorishek et al;and U.S. Pat. No. 6,463,582, entitled “Dynamic Optimizing Object CodeTranslator for Architecture Emulation and Dynamic Optimizing Object CodeTranslation Method”, by Lethin et al; and U.S. Pat. No. 5,790,825,entitled “Method for Emulating Guest Instructions on a Host ComputerThrough Dynamic Recompilation of Host Instructions”, by Eric Traut, eachof which is hereby incorporated herein by reference in its entirety; andmany others, illustrate a variety of known ways to achieve emulation ofan instruction format architected for a different machine for a targetmachine available to those skilled in the art.

In FIG. 15, an example of an emulated host computer system 5092 isprovided that emulates a host computer system 5000′ of a hostarchitecture. In the emulated host computer system 5092, the hostprocessor (CPU) 5091 is an emulated host processor (or virtual hostprocessor) and comprises an emulation processor 5093 having a differentnative instruction set architecture than that of the processor 5091 ofthe host computer 5000′. The emulated host computer system 5092 hasmemory 5094 accessible to the emulation processor 5093. In the exampleembodiment, the memory 5094 is partitioned into a host computer memory5096 portion and an emulation routines 5097 portion. The host computermemory 5096 is available to programs of the emulated host computer 5092according to host computer architecture. The emulation processor 5093executes native instructions of an architected instruction set of anarchitecture other than that of the emulated processor 5091, the nativeinstructions obtained from emulation routines memory 5097, and mayaccess a host instruction for execution from a program in host computermemory 5096 by employing one or more instruction(s) obtained in asequence & access/decode routine which may decode the hostinstruction(s) accessed to determine a native instruction executionroutine for emulating the function of the host instruction accessed.Other facilities that are defined for the host computer system 5000′architecture may be emulated by architected facilities routines,including such facilities as general purpose registers, controlregisters, dynamic address translation and I/O subsystem support andprocessor cache, for example. The emulation routines may also takeadvantage of functions available in the emulation processor 5093 (suchas general registers and dynamic translation of virtual addresses) toimprove performance of the emulation routines. Special hardware andoff-load engines may also be provided to assist the processor 5093 inemulating the function of the host computer 5000′.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of one or more aspects of the present inventionhas been presented for purposes of illustration and description, but isnot intended to be exhaustive or limited to the invention in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art without departing from the scope and spiritof the invention. The embodiment was chosen and described in order tobest explain the principles of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand the invention for various embodiment with variousmodifications as are suited to the particular use contemplated.

What is claimed is:
 1. A computer program product for executing a machine instruction in a central processing unit, the computer program product comprising: a computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: obtaining a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field to provide an opcode, the opcode identifying a convert from zoned to decimal floating point function; a first register field designating a first operand location; a second register field and a displacement field, wherein contents of a second register designated by the second register field are combined with contents of the displacement field to form an address of a second operand; and a sign control used to indicate whether the second operand has a sign field; and executing the machine instruction, the executing comprising: converting the second operand in a zoned format to a decimal floating point format, wherein the converting comprises converting zoned digits in the second operand to one or more densely packed decimal groups of a result, and converting zoned data in the second operand to a bit sequence of the result; and placing the result in the first operand location, wherein the result is stored to the location in the decimal floating point format absent issuing one or more additional machine instructions to convert to the decimal floating point format.
 2. The computer program product of claim 1, wherein the opcode, when a first value, indicates a zoned source and a long decimal floating point result.
 3. The computer program product of claim 1, wherein the opcode, when a second value, indicates a zoned source and an extended decimal floating point result.
 4. The computer program product of claim 1, wherein the sign control is specified in a mask field of the machine instruction.
 5. The computer program product of claim 1, wherein the machine instruction further includes a length field specifying a length of the second operand.
 6. The computer program product of claim 1, wherein the executing further comprises reading the second operand from memory, and performing the converting on the second operand read from memory.
 7. The computer program product of claim 1, wherein the executing further comprises determining a sign for the result, and wherein the placing comprises including the determined sign with the result in the first operand location.
 8. The computer program product of claim 7, wherein the determining is based on the sign control.
 9. The computer program product of claim 8, wherein based on the sign control being a first value, the determining comprises: reading a sign field from memory, the sign field being included in the second operand; and setting the sign from the sign field.
 10. The computer program product of claim 8, wherein based on the sign control being a second value, the determining comprises forcing a positive sign for the result.
 11. A computer system for executing a machine instruction in a central processing unit, the computer system comprising: a memory; and a processor in communications with the memory, wherein the computer system is configured to perform a method, said method comprising: obtaining a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field to provide an opcode, the opcode identifying a convert from zoned to decimal floating point function; a first register field designating a first operand location; a second register field and a displacement field, wherein contents of a second register designated by the second register field are combined with contents of the displacement field to form an address of a second operand; and a sign control used to indicate whether the second operand has a sign field; and executing the machine instruction, the executing comprising: converting the second operand in a zoned format to a decimal floating point format, wherein the converting comprises converting zoned digits in the second operand to one or more densely packed decimal groups of a result, and converting zoned data in the second operand to a bit sequence of the result; and placing the result in the first operand location, wherein the result is stored to the location in the decimal floating point format absent issuing one or more additional machine instructions to convert to the decimal floating point format.
 12. The computer system of claim 11, wherein the opcode, when a first value, indicates a zoned source and a long decimal floating point result.
 13. The computer system of claim 11, wherein the opcode, when a second value, indicates a zoned source and an extended decimal floating point result.
 14. The computer system of claim 11, wherein the sign control is specified in a mask field of the machine instruction.
 15. The computer system of claim 11, wherein the machine instruction further includes a length field specifying a length of the second operand.
 16. The computer system of claim 11, wherein the executing further comprises reading the second operand from memory, and performing the converting on the second operand read from memory.
 17. The computer system of claim 11, wherein the executing further comprises determining a sign for the result, and wherein the placing comprises including the determined sign with the result in the first operand location.
 18. The computer system of claim 17, wherein the determining is based on the sign control.
 19. The computer system of claim 18, wherein based on the sign control being a first value, the determining comprises: reading a sign field from memory, the sign field being included in the second operand; and setting the sign from the sign field.
 20. The computer system of claim 18, wherein based on the sign control being a second value, the determining comprises forcing a positive sign for the result. 